9,100 research outputs found
Optimal Accomplice-Witnesses Regulation under Asymmetric Information
We study the problem of a Legislator designing immunity for privately informed cooperating accomplices. Our objective is to highlight the positive (vertical) externality between expected returns from crime and the information rent that must be granted by the Legislator to whistleblowers in order to break their code of silence (omertà ) and elicit truthful information revelation. We identify the accomplices' incentives to release distorted information and characterize the second-best policy limiting this behavior. The central finding is that this externality leads to a second-best policy that purposefully allows whistleblowers not to disclose part of their private information. We also show that accomplices must fulfill minimal information requirements to be admitted into the program (rationing), that a bonus must be awarded to accomplices providing more reliable information and that, under some conditions, rewarding a self-reporting `boss' can increase efficiency. These results are consistent with a number of widespread legislative provisions.Accomplice-witnesses, Adverse Selection, Leniency, Organized Crime
Impacts of fragmented accretion streams onto Classical T Tauri Stars: UV and X-ray emission lines
Context. The accretion process in Classical T Tauri Stars (CTTSs) can be
studied through the analysis of some UV and X-ray emission lines which trace
hot gas flows and act as diagnostics of the post-shock downfalling plasma. In
the UV band, where higher spectral resolution is available, these lines are
characterized by rather complex profiles whose origin is still not clear.
Aims. We investigate the origin of UV and X-ray emission at impact regions of
density structured (fragmented) accretion streams.We study if and how the
stream fragmentation and the resulting structure of the post-shock region
determine the observed profiles of UV and X-ray emission lines.
Methods. We model the impact of an accretion stream consisting of a series of
dense blobs onto the chromosphere of a CTTS through 2D MHD simulations. We
explore different levels of stream fragmentation and accretion rates. From the
model results, we synthesize C IV (1550 {\AA}) and OVIII (18.97 {\AA}) line
profiles.
Results. The impacts of accreting blobs onto the stellar chromosphere produce
reverse shocks propagating through the blobs and shocked upflows. These
upflows, in turn, hit and shock the subsequent downfalling fragments. As a
result, several plasma components differing for the downfalling velocity,
density, and temperature are present altoghether. The profiles of C IV doublet
are characterized by two main components: one narrow and redshifted to speed
50 km s and the other broader and consisting of subcomponents
with redshift to speed in the range 200 400 km s. The profiles
of OVIII lines appear more symmetric than C IV and are redshifted to speed
150 km s.
Conclusions. Our model predicts profiles of C IV line remarkably similar to
those observed and explains their origin in a natural way as due to stream
fragmentation.Comment: 11 pages, 10 figure
Accretion disk coronae of Intermediate Polar Cataclysmic Variables - 3D MagnetoHydro-Dynamic modeling and thermal X-ray emission
IPCVs contain a magnetic, rotating white dwarf surrounded by a magnetically
truncated accretion disk. To explain their strong flickering X-ray emission,
accretion has been successfully taken into account. Nevertheless, observations
suggest that accretion phenomena could not be the only process behind it. An
intense flaring activity occurring on the surface of the disk may generate a
corona, contribute to the thermal X-ray emission and influence the system
stability. Our purposes are: investigating the formation of an extended corona
above the accretion disk, due to an intense flaring activity occurring on the
disk surface; studying its effects on the disk and stellar magnetosphere;
assessing its contribution to the observed X-ray flux. We have developed a 3D
MHD model of a IPCV. The model takes into account gravity, disk viscosity,
thermal conduction, radiative losses and coronal flare heating. To perform a
parameter space exploration, several system conditions have been considered,
with different magnetic field intensity and disk density values. From the
results of the evolution of the model, we have synthesized the thermal X-ray
emission. The simulations show the formation of an extended corona, linking
disk and star. The flaring activity is capable of strongly influencing the disk
configuration and its stability, effectively deforming the magnetic field
lines. Hot plasma evaporation phenomena occur in the layer immediately above
the disk. The flaring activity gives rise to a thermal X-ray emission in both
the [0.1-2.0] keV and the [2.0-10] keV bands. An intense coronal activity
occurring on the disk surface of an IPCV can affect the structure of the disk
depending noticeably on the density of the disk and the magnetic field of the
central object. Moreover, the synthesis of the thermal X-ray fluxes shows that
this flaring activity may contribute to the observed thermal X-ray emission
Follicular size affects the meiotic competence of in vitro matured prepubertal and adult oocytes in sheep
Non-atretic follicles dissected from prepubertal and adult ovaries were allocated in three groups: a) < 1 mm; b) 1-2 mm; c) > 2 mm. After 24 h of maturation, a lower percentage of adult oocytes from group a (P < 0.01) reached metaphase II than those from groups b and c (70.4 versus 89.5 and 95.5). Prepubertal oocytes showed similar results (P < 0.01; 27.2 versus 79.8 and 81.8). There was a significant difference (P < 0.01) in meiotic progression between prepubertal and adult oocytes of < 1 mm follicles. The diameter of prepubertal oocytes derived from group a was significantly lower (P < 0.01) compared to groups b and c (138.1 versus 142.1 and 145.6); adult oocytes showed similar results (P < 0.01; 142.2 versus 157.2 and 158.1 Oocytes with the same diameter derived from different follicles of prepubertal and adult ovaries showed similar meiotic progression rates.
Des follicules non-atrétiques sélectionnés à partir d’ovaires d’ovins prépubères et adultes ont été répartis en trois groupes selon leur diamètre : a) < 1 mm ; b) 1-2 mm ; c) > 2 mm. Après 24 h de maturation les ovocytes dérivant des ovaires d’animaux adultes appartenant au groupe a ont atteint la MII dans des pourcentages nettement inférieurs (p < 0,01) à ceux observés pour les groupes b et c (70,4 versus 89,5 et 95,5). Des résultats identiques ont été obtenus avec les ovocytes provenant d’animaux prépubères (p < 0,01 ; 27,2 versus 79,8 et 81,8). Une grande différence (p < 0,01) dans le potentiel à reprendre la méiose existe entre les ovocytes de prépubères et des adultes provenant de follicules < 1 mm. Le diamètre des ovocytes d’agneaux provenant de follicules du groupe a était nettement inférieur (p < 0,01 ) par rapport à ceux provenant de follicules des groupes b ou c (138,1 versus 142,1 et 145,6). Des résultats identiques ont été observés pour les ovocytes provenant d’animaux adultes (p < 0,01, 142,2 versus 157,2 et 158,1). Des ovocytes de même diamètre provenant d’ovaires de prépubères et d’adultes ne diffèrent pas dans leur aptitude à reprendre la méiose
Accomplice-Witnesses, Organized Crime and Corruption: Theory and Evidence from Italy
Since 1991 the Italian Legislator grants amnesties, protection and even economic bene.ts to former mobsters cooperating with the justice. These incentives were intro- duced to break down omertà . What is the economic logic behind this policy? Did the program succeed? To address these issues we develop a model accounting for the main trade-o¤s involved in the introduction of accomplice-witnesses regulations. We argue that rewarding informants is sometimes necessary to .ght organized crime and show how the optimal amnesty varies with the e¤ectiveness of the protection program, the reliability of the informants.testimonies, the strength of external complicities, and the internal cohesion between criminal partners. The optimal policy sti.es crime, spurs prosecution and induce a negative relationship between the number of talkers and the conviction rate. The available evidence supports the model.s predictions.Accomplice-witnesses, Criminal Organizations, Leniency, Whistle-Blower
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